For the purpose of fully explaining about the level of technology at present with regard to the present application, it should be noted that all explanation in the documents such as patents, patent applications, patent publications and science papers cited or specified in the present application is incorporated into the present application by referring them.
The high integration of the semiconductor device has been achieved through the lithography technology for forming a minute pattern and the etching technology. However, as thus high performance of the semiconductor device progresses, it follows that the manufacturing cost increases because of sophisticated manufacturing processes.
So, recently it is desired to drastically reduce manufacturing cost of the semiconductor device and to shorten the whole number of processes through integrating the process for manufacturing the contact hole patterns by conducting (1) to form a minute contact hole, as a first challenge, (2) to create a contact hole with forward tapered, as a second challenge and (3) to form a plurality of contact holes with different depth or aspect ratio in one time process of lithography, as a third challenge.
In realizing to form the minute contact hole as the first challenge mentioned above it is already known that a transformed resist can be formed through the process that causes thermal reflow in an organic film by further heat treatment after patterning by means of exposing a resist made of the organic film and processing procedure to it.
And then it is possible to form the contact hole with minute dimensions which exceeds exposure limit, by etching using this transformed resist
This first prior art will be explained referring to the drawings. FIGS. 1A to 1D are partial longitudinal sectional views illustrating a series of processes for forming minute contact holes that utilizes thermal reflow of a resist film made of an organic film with regard to the first prior art
As illustrated in FIG. 1A, a gate electrode 102 is selectively formed on a substrate 101. Then, a first interlayer insulating film 103 is formed on the substrate 101 and the gate electrode 102. Further, a resist mask 106 is formed on the first interlayer insulating film 103 through a process of coating a resist film made of an organic film on the first interlayer insulating film 103 and exposing the resist film and then processing procedure to it. In the case, the limit of the dimension D1 in the opening portion of the resist mask 106 depends on the limit of exposure.
As illustrated in FIG. 1B, to reduce the dimension D1 in the opening portion of the resist mask 106 to the extent smaller than the limit of exposure, thermal reflow in the resist mask 106 is caused through heat treatment to whole the substrate 101 at a temperature in the range of 150° C. to 200° C., thereby the dimension D1 in the opening portion of the resist mask 106 diminishes in size to the dimension D2, where the dimension D2 is smaller than the dimension D1. As the result a resist mask 107 is formed, which is transformed through thermal reflow and is provided with the opening portion with the minute dimension D2 exceeding the limit of exposure.
As illustrated in FIG. 1C, a contact hole 108 reaching the gate electrode 102 is formed through etching the first interlayer insulating film 103 using the resist mask 107 with the opening portion of the dimension D2, transformed by thermal reflow. Since the dimension of this contact hole 108 depends on the dimension D2 in the opening portion of the thermal reflow resist mask 107, it is possible to form the contact hole with much more minute dimension, compared with a contact hole not treated with thermal reflow of a resist mask.
As illustrated in FIG. 1D, a substrate is formed by removing the thermal reflow resist mask 107 using the known method, which is provided with the contact hole 108 defined by the minute dimension D2 exceeding the limit of exposure. Then, using the known manufacturing method, the substrate is formed to a target product of the semiconductor device.
In the next, the prior art with regard to a contact hole with forward tapered, as the second challenge, will be explained.
A contact hole with a little forward tapered is formed by etching using the resist mask formed by the known lithography method without change.
This second prior art will be explained referring to the drawings.
FIGS. 2A to 2C are partial longitudinal sectional views illustrating a series of processes for forming contact holes, using the resist mask formed by the known process of lithography with regard to the second prior art without change.
As illustrated in FIG. 2A, a gate electrode 202 is selectively formed on a substrate 201. Then, a first interlayer insulating film 203 is formed on the substrate 201 and the gate electrode 202. Further, a second interlayer insulating film 204 is formed on the first interlayer insulating film 203. Thereafter, a resist mask 206 is formed on the second interlayer insulating film 204 through coating a resist film made of an organic film on the second interlayer insulating film 204, and conducting the exposing procedure of the resist film and then the processing procedure to it which are the known lithography process, wherein the opening portion of the resist mask 206 is a little forward tapered. Namely, the dimension of the opening portion in the horizontal direction decreases a little as the depth increases.
As illustrated in FIG. 2B, the second interlayer insulating film 204 is etched using the resist mask 206. In this case the resist mask 206 becomes a resist mask 207 with the surface removed a little, through removing the surface of the resist mask 206 a little and retracting the side wall facing to the opening portion of the resist mask 206. The dotted line in FIG. 2B shows a longitudinal cross sectional shape of the resist mask 206 before it is etched. At this time the hole formed in the second interlayer insulating film 204 is slightly forward tapered. Namely, the dimension in horizontal direction of the opening portion decreases a little as the depth increases.
As illustrated in FIG. 2C, a contact hole reaching the gate electrode 202 is formed through etching the first interlayer insulating film 203 using the resist mask 207 which surface is a little removed. In this case the resist mask 207 becomes a resist mask 208 with the surface further removed, through further removing the surface of the resist mask 207 and further retracting the side wall facing to the opening portion of the resist mask 207. The dotted line in FIG. 2C shows a longitudinal cross sectional shape of the resist mask 207 before it is etched.
It is apparent that the surface of the resist mask 208 illustrated in FIG. 2C shows the surface of the resist mask 207 illustrated in FIG. 2B further removed and also the side wall illustrated in FIG. 2B further retracted. At this time, a contact hole 209 formed in the first interlayer insulating film 203 and the second interlayer insulating film 204 is slightly forward tapered.
Through tapering forward slightly, the dimension of the contact hole 209 at the bottom diminishes slightly in size compared with the dimension at the upper part.
Then, a substrate is formed by removing the resist mask 208 using the known method, which is provided with the contact hole 209 slightly forward tapered. Then, using the known manufacturing method, the substrate is formed to a target product of the semiconductor device.
In the third, the prior art with regard to forming a plurality of contact holes with different depth or aspect ratio in one time process of lithography, as a third challenge, will be explained.
The third prior art will be explained referring to the drawings.
FIGS. 3A to 3D are partial longitudinal sectional views illustrating a series of processes for forming a plurality of contact holes with different depth in one time process of lithography with regard to the third prior art.
As illustrated in FIG. 3A, a first electrode 302 is selectively formed on a substrate 301. Then, a first interlayer insulating film 303 is formed on the substrate 301 and the first electrode 302. Then, a second electrode 305 is selectively formed on the first interlayer insulating film 303. As shown in the figure, here, the location of the second electrode 305 in the horizontal direction differs from that of the first electrode 302. Further, a second interlayer insulating film 304 is formed on the first interlayer insulating film 303 and the second electrode 305.
Thereafter, a resist mask 306 is formed on the second interlayer insulating film 304 through coating a resist film made of an organic film on the second interlayer insulating film 304, and conducting the exposing procedure of the resist film and then the processing procedure to it, which are the known lithography process, wherein the resist mask 306 is provided with a first opening portion 306-1 and a second opening portion 306-2. The first opening portion 306-1 is located in the upper side C2 of the first electrode 302, and the second opening portion 306-2 is located in the upper side C1 of the second electrode 305. As shown in the figure, the dimension D1 in the horizontal direction of the first opening portion 306-1 is larger than the dimension D2 in the horizontal direction of the second opening portion 306-2.
As illustrated in FIG. 3B, a first contact hole 307 and a second contact hole 308 are formed through etching the second interlayer insulating film 304 and the first interlayer insulating film 303 using the resist mask 306.
As shown in the figure, the first contact hole 307 is formed to be consistent with the first opening portion 306-1 of the resist mask 306, and reaches the surface of the first electrode 302 passing through the second interlayer insulating film 304 and the first interlayer insulating film 303.
And, the depth d1 of the first contact hole 307 corresponds to the value obtained by subtracting the thickness of the first electrode 302 from the sum of each thickness of the first interlayer insulating film 303 and the second interlayer insulating film 304. Further, the dimension of the first contact hole 307 in the horizontal direction is defined by the dimension D1 in the horizontal direction of the first opening portion in the resist mask 306.
On the other hand, the second contact hole 308 is formed to be consistent with the second opening portion 306-2 of the resist mask 306, and reaches the surface of the second electrode 305 passing through the second interlayer insulating film 304.
And, the depth d2 of the second contact hole 308 corresponds to the value obtained by subtracting the thickness of the second electrode 305 from the thickness of the second interlayer insulating film 304. Namely, the depth d2 of the second contact hole 308 is shallower than the depth d1 of the first contact hole 307(d1>d2).
Further, the dimension of the second contact hole 308 in the horizontal direction is defined by the dimension D2 in the horizontal direction of the second opening portion 306-2 in the resist mask 306.
As stated previously, the first contact hole 307 and the second contact hole 308 are formed by the same etching process using the same resist mask 306. In this case when the etching depth reaches d2 in the location of C1, the surface of the second electrode 305 is revealed, and as the result, the second contact hole 308 is formed, and the etching operation in C1 should be the state of etching off.
On the other hand, in the location of C2 at that time the second interlayer insulating film 304 is not completely removed and moreover the first interlayer insulating film 303 is not yet etched. Accordingly, the etching operation in C2 continues until the surface of the first electrode 302 is revealed. Thus, the etching process terminates when the first interlayer insulating film 303 is etched, and the surface of the first electrode 302 is revealed, thereby forming the first contact hole 307.
In the case, there is a problem that the revealed surface of the second electrode 305 is subjected to damage through over etching in the etching operation until the surface of the first electrode 302 is revealed after the surface of the second electrode 305 has been revealed. Because the first electrode 302 and the second electrode 305 are made of materials such as metals which etching rate are substantially small compared with those of the first interlayer insulating film 303 and the second interlayer insulating film 304, the second contact hole 308 is not formed passing through the second electrode 305. However, as stated, the revealed surface of the second electrode 305 is continued to be disposed by etching until the surface of the first electrode 302 is revealed. For example, the revealed surface of the second electrode 305 is subjected to damage through over etching by the time interval (T2−T1) from the time T1 when the surface of the second electrode 305 is revealed to the time T2 when the surface of the first electrode 302 is revealed.
As illustrated in FIG. 3C, the resist mask 306 is removed by the known method. Then, as illustrated in FIG. 3D, a first wiring layer 309 and a second wiring layer 310 are formed by the known method. In this case, the first wiring layer 309 lies with the spread on the revealed surface of the first electrode 302 and along the side wall of the first contact hole 307. On the other hand, the second wiring layer 310 lies with the spread on the revealed surface of the second electrode 305 which was exposed through over etching, and along the side wall of the second contact hole 308.
As the result, a substrate provided with the first contact hole 307 and the second contact hole 308 is formed wherein the first contact hole 307 is formed to have a deep hole with the depth of d1 reaching the first electrode 302, and the second contact hole 308 is formed to have a shallow hole with the depth of d2 reaching the second electrode 305 exposed through over etching.
Thereafter, the target semiconductor is manufactured by the known method. This third prior art is illustrated in FIG. 15 of the Japanese patent No. 3,208,658 as the contact holes 42 and 43.
Referring to FIGS. 1A to 1D, the first prior art mentioned above discloses that the contact hole with the minute dimension exceeding the limit of exposure is formed through etching using as a mask the transformed resist film obtained by transforming an organic resist film through the thermal reflow. However, the first prior art making use of the thermal reflow includes the following drawback.
1) The first problem is that in case of unevenness in the photo resist width, the degree of tapering in photo resist patterns after the thermal reflow becomes uneven because the shape at the reflow portion depends on the width of photo resist patterns.
2) The second problem is that tapering by thermal reflow involves diminishing of the dimension of the photo resist pattern in the horizontal direction. The thermal reflow causes to increase the dimension in the horizontal direction, while the organic pattern involves contraction in volume when it is subjected to heat treatment. Namely, there exists a limitation in increasing the dimension in the horizontal direction, because the thermal reflow causes contraction in volume of the organic pattern due to heat, in addition to increase of the dimension in the horizontal direction due to fluidization.
3) The third problem is that because the thermal reflow is a reflow with high viscosity, the front shape of the reflow becomes undulant and uneven, and as the result, such mask due to the thermal reflow for etching allows often to form side etching, thereby causing wiring with inadequate tapered shape, that is, the cross section of the wiring with the shape of vertical or partially reverse tapered.
Also, referring to FIGS. 2A to 2C, the second prior art mentioned above discloses that the contact hole with forward tapered though only a little by conducting etching using the resist mask formed by the known process of lithography without changing the resist mask. However, the second prior art includes the following drawback. Namely, the degree of angle of the tapered shape in the contact hole with the forward tapered shape due to the second prior art is only a little, and therefore it is impossible for the second prior art to be applied to forming a contact hole necessary for a large or significant forward tapering.
Referring to FIGS. 3A to 3D, the third prior art mentioned above discloses that a plurality of contact holes with different depth are formed in one time process of lithography. However, the third prior art includes the following drawback.
As stated previously, because the shallow contact hole is exposed through over etching the following two problems arise. The first problem is that the surface of the second electrode to which the shallow contact hole reaches is subjected to heavy damage by over etching, and later that causes burnout failure in the second wiring lying with the spread on the surface of the second electrode and along the side wall of the shallow contact hole, and causes increase of contact resistance between the second wiring and the surface of the second electrode.
The second problem is that forming forward tapered shape of the contact hole becomes difficult. This is caused in a way that the side wall adjacent to the bottom of the shallow contact hole is over etched, then the side wall in the lower area of the contact hole retracts outwardly in the horizontal direction, and then the side wall of the contact hole is formed to be vertical gradually, which has with a slope at first, even if the shallow contact hole has been formed with forward tapered shape.
As the countermeasures to the first and second problems with regard to the third prior art mentioned above, it is presumable that the over etching in the shallow contact hole is avoided by means of delaying the starting time of etching to form the shallow contact hole than the starting time of etching to form the deep contact hole, using a half exposure method. The half exposure technology is disclosed in the Japanese laid open patent No. 2000-164584. This half exposure technology will be explained as the fourth prior art in below.
Specifically, a resist mask provided with a first opening portion and a thin portion in film thickness is formed making use of the half exposure technology. Then, the first opening portion is aligned to a position in which the deep contact hole is formed, while the thin portion in film thickness is aligned to a position in which the shallow contact hole is formed. In the initial process of etching, etching operation through the first opening portion is conducted for only forming the deep contact hole using the resist mask provided with the first opening portion and the thin portion in film thickness.
Then, at the time when the etched depth reaches a given depth to form the deep contact hole, the etching operation is interrupted, and then a second opening portion is formed through removing the thin portion in film thickness. And in addition to restart etching operation for the deep contact hole a new etching operation starts to form the shallow contact hole, using the transformed resist mask provided with the first and second opening portions. Both of etching to form the deep contact hole and etching to form the shallow contact hole are conducted at the same time. Both of etching to form contact holes, each having different depth, can be terminated at the same time, for example, in case that the given depth is defined as the difference between the depth of the deep contact hole and the depth of the shallow contact hole. Accordingly, it is possible to avoid the first and the second problems with regard to the third prior art because no over etching occurs.
However, the fourth prior art, though it makes use of the half exposure technology, still includes the following drawback. As stated previously, it is necessary to prepare the resist mask which is provided with the first opening portion and the thin portion in film thickness is formed, making use of the half exposure technology. Accordingly, the number of processes for manufacturing increases, compared with the ordinary cases in which a resist mask is made of the same film thickness, and then the manufacturing cost increases. Also, further processes are required to remove the thin portion in film, thickness of the resist mask and then to form the second opening portion that leads to increase of the number of manufacturing process and the cost.
Accordingly, it has been desired to provide a novel method for forming a contact hole without drawbacks and problems included in the prior arts mentioned above.